Vehicle airbag systems are known in the art and have been credited with greatly increasing the overall safety of motor vehicles. Specifically, these airbag systems are designed such that during an accident, one or more airbags will be rapidly inflated and will be positioned between the vehicle occupant and the hard surfaces of the vehicle interior. These inflated airbags will inhibit the vehicle occupant from impacting the interior surfaces of the vehicle and will thus greatly reduce the likelihood that the occupant will experience significant injuries in the crash.
As is known in the art, airbag systems will generally include an inflator that is capable of rapidly producing a large quantity of gas. As its name implies, the purpose of the inflator is to “inflate” the airbag. When an accident occurs, the inflator will rapidly produce a large quantity of gas that is then channeled into the airbag. In turn, such rapid influx of gas inflates and expands the airbag and causes the airbag to become positioned in front of one or more of the interior surfaces of the vehicle. As accidents occur quickly, this inflation of the airbag must occur very rapidly—i.e., generally within approximately 100 to 150 milliseconds.
Many currently used inflators are referred to as “pyrotechnic” inflators in that these devices create the large quantity of gas via a pyrotechnic material. Pyrotechnic materials are generally solid materials that are designed such that when ignited, they undergo a chemical reaction that results in the production of a gaseous product. One of the first pyrotechnic materials used was sodium azide (NaN3) which is a solid, white compound that may be ignited/combusted to produce large quantities of nitrogen gas (N2). Other pyrotechnic materials have also been used. As is known in the art, the pyrotechnic materials used in inflators are generally selected such that the resulting gas produced in the chemical reaction is non-toxic and non-corrosive and thus may be safely used/inhaled by humans.
As experience with pyrotechnic inflators has increased, new and additional pyrotechnic materials have been developed to meet the needs of a particular application. For example, many pyrotechnic materials are pressed into “wafer” shapes so that they may be easily stacked or arranged in the inflator. Examples of such types of wafer shapes may be found in U.S. Pat. Nos. 5,551,343, 4,817,828, and 5,367,872, which patents are expressly incorporated herein by reference.
Other types of pyrotechnic materials include one or more additives that are designed to change the chemical properties of the composition. For example, various types of “flexible” pyrotechnic materials have been developed by adding silicon or other types of rubberized binder materials to the overall pyrotechnic composition. These additives are often referred to as “flexible binding materials.” After the flexible binding material has been added, the resulting pyrotechnic material is a relatively pliant material that may be used in situations (such as “side-curtain” airbag systems) in which the inflator must fit into curved, tightly-packed vehicle surfaces.
Unfortunately, the inclusion of flexible binding materials within the pyrotechnic materials results in unwanted consequences. For example, during ignition/combustion of the pyrotechnic material, the flexible binding materials will also undergo a chemical reaction and will produce a product that is undesirable and must be dealt with appropriately.
Perhaps more importantly, the addition of flexible binding materials to the pyrotechnic material may affect the burn rate of the pyrotechnic material. The burn rate of the pyrotechnic material measures how fast the solid pyrotechnic material will react to form the gaseous product. As noted above, most airbag applications require a sufficient burn rate such that the airbag will be inflated in 150 milliseconds or less. As flexible binding materials generally do not burn or react as rapidly as sodium azide (or other pyrotechnics), the addition of such silicon/rubberized materials will generally slow down the burn rate of the pyrotechnic composition.
This slowing of the pyrotechnics' burn rate is a significant concern to airbag/vehicle manufacturers. In fact, manufacturers will often take steps (such as using larger inflators, increasing the amount of the pyrotechnic material, etc.) to ensure that, despite any reduction in burn rate caused by the introduction of a silicon/rubberized binder material, the airbag will still inflate in a timely manner. While measures such as increasing the size of the inflator or the amount of the pyrotechnic material do compensate for the reduction in burn rate, such measures will greatly increase the overall cost and complexity of the airbag systems and are thus not preferred. Increased pyrotechnic material will also lead to an increase in undesirable products of combustion, or effluent values, which is clearly not preferred.
Accordingly, it would be a benefit in the art to provide a new type of pyrotechnic material that would address one or more of the above-recited concerns. Such a pyrotechnic material is disclosed herein.